Conceição Lopes

PTPlan MPLS: a tool for MPLS network dimensioning

This paper presents a tool for MPLS network dimensioning that allows for multi-hour dimensioning of networks supporting simultaneously peer-to-peer and client-server services. The dimensioning model is able to take into account several LSP attributes: degree of survivability (link disjoint and node disjoint cases), maximum hop count, usable colours and preferred routes. The dimensioning problem is a combined capacity design and routing problem where the LSP sets are calculated in order to minimise the network operational costs. This problem is formulated as an integer programming problem, which is solved through an heuristic based on Lagrangean relaxation with sub-gradient optimisation. The network design tool, named PTPlan MPLS, includes a graphical interface for an easy introduction and edition of the network parameters. Results show that the tool can design networks of realistic size in seconds using a standard PC platform.

Throughput assessment of TCP over distributed WiFi access networks supported by RoF

Presently, wireless local area networks (WLANs) are experiencing a tremendous increase of wireless bandwidth hungry devices and the increasing deployment of cloud-based enterprise networks. Additionally, mobile operators with heavily congested cellular networks are exploring the strategy of offload traffic from their cellular networks to WiFi hotspots. Technologies that were originally proposed for the mobile network, such as distributed antenna systems supported by radio over fiber (RoF) providing a distributed centrally managed network, can also improve the overall performance and efficiency of WLANs. However, it is important to find out if such network solutions can cope with the WiFi protocols. This paper presents a simulation based assessment of the downstream throughput performance provided by the TCP transport protocol when attached wireless users are connected to different remote antenna units (RAUs) on a distributed WiFi access network supported by RoF. The results show that throughput does not significantly decrease for RoF coverage radii of less than 10 kilometers. Moreover, the network throughput provided through different RAUs is not significantly different whatever is the length of the RoF link.

Combined link dimensioning and weight assignment of minimum weight routing networks

MPLS (multi-protocol label switching) technology provides the flexibility required for managing the way the traffic is routed through the network. However, label switched path (LSP) configuring is a hard task in a growing network, as more and more routes need configuring and monitoring. A viable alternative may be to rely on an IGP (interior gateway protocol) routing protocol to determine the paths to be used by the LSPs, thus freeing the operator from the manual configuring of all LSP paths. Here, we address the procedure of dimensioning a MPLS network where a minimum weight routing protocol (as OSPF or IS-IS) is used to determine the paths of the LSPs. We start by presenting the complete minimum weight routing network design problem (MWRNDP) with explicit minimum weight routing constraints. Then, we propose a two-step approach based on two ILP models which are a decomposition of the complete model in two separate optimization problems: first, we determine the physical network configuration and the traffic flow routing with the network design problem (NDP); then, we determine the link weights required to achieve the determined traffic routing with the link weight assignment problem (LWA). Because in the first problem the traffic routing is destination based, there may be instances where a minimum weight routing solution is not found. In these cases, an additional constraint is added to the first problem and the two-step approach is repeated. An important observation is that this methodology obtains the optimal solutions and the computational results show that it requires much lower computational times than the original global MWRNDP model. Using the two-step approach, a set of computational tests is presented to determine the cost penalty in MPLS network design when using minimum weight routing as opposed to source based routing.